Development of an antioxidant assay to study oxidative potential of airborne particulate matter
Abstract. Oxidative potential is a measure of redox activity of airborne particulate matter (PM) and is often used as a surrogate to estimate one form of PM toxicity. The evaluation of oxidative potential in a physiologically relevant environment is always challenging. In this work, we developed a chromatographic method, employing an ultra-high-performance liquid chromatograph coupled to a triple–quadruple mass spectrometer, to determine the oxidative potential of PM from different sources. To this purpose, we measured the PM-induced oxidation of glutathione, cysteine, and ascorbic acid, and formation of glutathione disulfide and cystine, following PM addition to simulated epithelial lining fluids, which, in addition to the antioxidants, contained inorganic salts, a phospholipid, and proteins. The new method showed high precision and, when applied to standard reference PM, the oxidative potential was found to increase with the reaction time and PM concentration in the lung fluid. The antioxidant depletion rates were considerably higher than the rates found with the conventional dithiothreitol assay, indicating the higher sensitivity of the new method. The presence of the lung fluid inorganic species increased the oxidative potential determined through glutathione and cysteine, but showed an opposite effect with ascorbic acid, whereas the presence of proteins resulted in a moderate decrease in the oxidative potential. In the presence of PM2.5, glutathione and cysteine demonstrated similar depletion patterns, which were noticeably different from that of ascorbic acid, suggesting that cysteine could be used as an alternative to glutathione for probing oxidative potential.